central heating problem

Hi All
I was so impressed with the help everyone is offering, I thought Id
ask if anyone had any ideas about whats the problem with mine..
Standard non-sealed sytem with Ideal classic boiler, Grundfoss 15-20
pump, Honeywell roomstat running 10 rads.
We had a problem with sludge and got a plumber to pump it round and
the system has now been fully drained and refilled, and bled of air.
However, last week only the upstairs rads were working, and after
watching the system for a while we found the boiler only lights for
about 60 seconds then switches off.
Ive checked the pump is spinning ok, so Im stuck for ideas?
Could it be the impeller blades in the pump, or should I be looking at
the roomstat..(can I isolate it to see if thats the problem?
Any ideas gratefully received.
Many thanks
Maskie

We need to know a lot more about the design and layout of your system.
Is it fully pumped, or gravity hot water and pumped central heating? [Does
the pump run when just heating the HW, or only when the CH is on?]
If fully pumped, it's likely that you've got one or more motorised valves.
How many, and what type (2-port or 3-port)?
How is the central heating distributed? Do the main pipes go between the
floors, with pipes coming down from above to each downstairs rad - or do you
have separate upstairs and downstairs circuits with just 2 largish (22mm or
28mm) pipes going upstairs?
It will be much easier to suggest the likely cause if you answer the above
questions.

Roger
Thanks for the help. Its gravity HW and pumped CH - pump only runs
when heating is on.
Problem is, I cant find any motorized valves........duh.....Ive looked
along every piece of the pipes run from boiler to loft and no joy.
AS far as pipework is concerned, there is a separate run going
upstairs....the 2 largish pipes you suggested, going upstairs.
Many thanks again
Maskie

If it's gravity HW, there almost certainly won't be any motorised valves.
My best guess is that you have a problem with the pump. The shaft may be
turning, but perhaps the impellor isn't.
Is the domestic hot water getting hot ok?
When the central heating is divided into upstairs and downstairs circuits,
just joined by 2 vertical pipes, it's not uncommon for the upstairs rads to
get hot by gravity (convection) circulation, without the pump running - but
the downstairs rads won't get hot.

Log in

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.